This invention relates to a process for dyeing molded articles of polyoxymethylene resins with disperse dyes, and to the products obtained by this process.
Molded articles of polyoxymethylene resins are used as so-called engineering resins in various fields because of their excellent strength, friction- and abrasion-resistant properties, creep properties, fatigue properties and electrical properties.
Colored articles are employed in many of these utilities. The molded articles of polyoxymethylene resins are usually colored by organic or inorganic pigments. In one method, they are colored by using colored pellets which have previously been prepared by mixing the resins with a pigment of the desired coloring in an extruder. In another method, colored articles are molded by feeding pellets covered with a pigment directly into an injection molding machine. However, these methods have several disadvantages. In the former case, for example, it is necessary to have in stock the pellets of various colors. The latter case involves problems such as the tainting of articles with another pigment on the molding machine hopper and ill-dispersed pigments. Moreover, depending upon the types of pigments employed, some of the pigments used in these methods may adversely affect the thermal stability of the polymers, and cause problems such as decomposition at the time of molding.
Meanwhile, it has been attempted in some studies to dye the molded articles of polyoxymethylene resins with dyestuffs. See, for example, U.S. Pat. No. 3,134,636 and S. J. Barker and M. B. Price, "Polyacetals", ILIFFE Books, London, p. 138, Lines 10-26. According to the processes disclosed in these references, polyoxymethylene is dyed easily by disperse dyestuffs, but such dyestuffs are disadvantageous in that they are extracted with substances such as oils on the skin surface thereof, and such as dioctyl phthalate, in which these dyestuffs are soluble.
This problem must also be solved in those utilities where the molded articles of polyoxymethylene resins come in contact with polyvinyl chloride leather or other materials containing dyestuff-dissolving substances such as dioctyl phthalate. These fields of use include, e.g., the inner door handles of automobiles, ski bindings, toy parts, parts of construction materials, buttons, and slide fasteners for apparel. For this reason, these methods have not yet been commercialized.